Inductive heating unit comprising coaxially arranged conductors



April 3, 1947- H. A. sTRlcKLAND, .n A 2,418,675

INDUCTIVE HEATING UNIT COMPRISINGCOAXIALLY ARRANGED CONDUGTORS 'Filedvlune 28, 1943 2 Sheets-Shee't 1 6 30 ,gnu/3 lll 5% 35. 3?

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1mm u A uw i@ mi 1 L A TTORNE/ April 8, 1947. H. A. sTRlcKLAND, JR

INDUCTIVE'HEATING UNIT COMPRISING COAX'IALLY ARRANGED CONDUCTORS Filed June 28, 1943 ATTORNEY Patented Apr. 8, 1947 INDUCTVE HEATlNG UNIT CGMPRISING COAXIALL f ARRANGED CONBUCTGRS Harold A. Strickland, Jr., Detroit, Mich., assigner, by mesne assignments, to rihe Budd Company, Philadelphia, Pa., a corporation of Pennsyl- Vania Application June 2s, 1943, serial No. 492,527

1 Claim.

This invention relates to induction apparatus for heat treating the inner surface of a tubular article. i

It is known in the field of inductive heating to utilize electro-magnetic induction for heating interior surfaces such as those of dies. For this purpose, however, use is made of current carrying coils the axes of which are, in general, parallel to that of the cylindrical area being heated. Consequently, the eddy current flow is circular and transverse to the zone axis.

In the present invention an important object is to employ the advantage in. interior zone heating of currents moving axial to the curved zone area. Another object is to provide an inductive heating means which increases the heating effect in the interior zone of concentric zones through geometric relationship of the zone surfaces. Still another object is to increase inductive heating effects through use of both geometric and proximity effects.

Additional objects of the invention include provision of novel means for supporting the workpiece and heating means, for insuring yieldable yet strong electrical contacts between workpiece and terminals, for insulating the electrical elements effectively, and other objects which will appear on consideration of the forms of the invention hereinafter described and shown in the accompanying drawings, in which:

Fig. 1 is a longitudinal section through the inductive heating unit;

Fig. 2 is a transverse section taken on lines .fl- 2 of Fig. l;

Fig. 3 is a longitudinal section through the con ductive heating unit;

Fig, 4 is a detail of the connector between electrode elements; and

Fig. 5 is a detail of a part of the cooling ymeans taken along lines 5 5 of Fig. 3.

Referring to Figure l there is disclosed a heating unit generally indicated by the numeral lil in which heat is applied to workpiece il by means of electro-magnetic induction solely, there being utilized in this form of the invention no metallic electrically conducting circuit between the workpiece and the conductors.

The heating unit is contained within an external metallic shell l2 which may be cylindrical in form and prior to assembly open at both ends,

the lower end being provided with an outwardly extending flange I3 apertured and screw-threaded to receive the machine screws It for holding the base plate I5 in fixed relationship to the shell I2. The base plate I5 as well as the shell l2 is of copper. In order to provide a path for the electric circuit as will appear hereinafter, this base plate l5 is centrally apertured to receive water coolant through conductor tube I5 which adjacent its lower end is fixed as by solder to the plate. The lower end of the conductor tube terminates in a section having an annular enlargement Il over which a rubber tubing i8 is adapted for positioning. a clamp ring i9 holding the tubing in place on the end of the tube IB. Above the base plate i5 the tube le projects axially within the shell l2 to a point above the same so as to obtain clearance for attachment to one branch. of the secondary electrical circuit.

The workpiece Il to be heat treated is shown as of cylindrical form with a central axial opening of a diameter suiiiciently increased over that of tub-e iii so as to provide a clearance 20 between the workpiece inner surface 2| and tube i6. As shown in Figure 1 the workpiece rests at its base upon the edge sections of insulating rings 22 made of any desirable heat resisting and insulating materials such as Transite or other asbestos containing compositions. As shown these insulating rings 22 have a larger radial depth than the rings 23 positioned opposite the workpiece. .also above the workpiece the insulating rings are of increased thickness So that they overlie the workpiece on their inner edges. Thus it is seen that the workpiece is snugly held within the shell I2 by the rings of insulating material 22, 23 and 2li. Attention is directed to the use of bolts 25 for binding together the lowermost insulating rings with the base plate I5 so that on removal of screws I4 the base plate with the four adjacent insulating rings may be removed as a unit with the center tube l t. By this means the workpiece. ll is exposed and may be removed or replaced.

The upper end of the shell i2 is closed by a centrally apertured metal plate 26 of copper, this pia-te being soldered or otherwise fastened to the shell i2 at its edge. To the central aperture of this top plate 26 is secured a tube 21 having an inner diameter substantially in excess of the tube l5 so that it may be positioned t0 include the tube l; and provide an exit'path for quench water. The upper end of the tube 2l terminates substantially below the end oi the tube lll and thereto is fixed by any appropriate means the end ring 2i? or the secondary terminal 2t. Directly above this terminal is the second secondary terminal which is provided with an clamp secured by the screw 3l to the upper end oi tube le. The two electrodes 29 and are spaced from each other by an insulation block the relative position of the block and terminals being ixed by means of machine bolts which pass through both terminals and the intervening blocli, the lower end of the screws being threaded directly into terminal 't while the sections ci the screws passing through the upper terminal are insulated therefrom by means of insulation tubes 34. The outer ends of the electrode terminals are attached to ter-v minal blocks 35 and 38, respectively, and to these blocks a secondary 31 of transformer 33 is attached. The transformer includes also the core 39 and primary 4G. The various elements of the primary circuit including power factor adjusting condensers are not disclosed as involving conventional apparatus.

As previously mentioned the central tube I6 combines the two functions of electrical current conduction and cooling fluid conduction, for the latter function the tube being connected to the rubber tubing I8, There is also provided a connection for introducing quenching fluid by means of the tube 4| fitted to a manifold I attached to the base plate i5 and provided with a rubber hose coupling at 42. The inlet connection of this tube 4| is through the manifold l, bese plate openings 5 to the space i3 defined by the tube |B and the inner edges of insulation rings 22. From Fig. l it appears that the space 43 communicates with the inner surface of the workpiece through the clearance space 25 between the workpiece and the tube |6.

In operation, with the workpiece inserted into the heating unit, as shown in Figure l, with the object of heat treating the inner surface 2| of the workpiece, the valvular' connector to the coolant source for the tube i6 is open to permit ingress of cooling fluid throughout the length of tube 6. The primary circuit is then closed introducing into the secondary circuit by transformer action current flow, alternating in character and preferably of low voltage and high amperage. Frequency of alternation of the current should be preferably in excess of 3000 cycles and much higher in certain instances. The path of the secondary current includes the tube |S, base plate |5, shell |2 and top plate 28, and the effect of a rapidly alternating high amperage current on this circuit is to induce currents in the metal workpiece l. Since the workpiece is closely adjacent the tube |55, the inductive effect of this tube is much more pronounced than the current in the shell l2 which is relatively distant from the workpiece. Since the current flow is axially along the tubing i5, the induced current now along the workpiece surface 2| is also axial in accordance with well known laws of electro-magnetic induction. Further, the skin and proximity effect resulting from the high frequency current tends to localize the current flow on the surface 2| giving a greater concentration of current at this surface than is present within the body of the workpiece. This concentration of current results not only from the skin and proximity effects but also from the geometric configuration of the workpiece. It appears from inspection that if the current flows axially along surface 2i, for a given current density now, a greater area is available at the cuter surface of the cylindrical workpiece on the inner surface 2| as indicated by dotted lines 4| in Figure 2. As a consequence, therefore, of this concentration of current now due to skin and proximity effects and geometric shape of the workpiece, the inner surface 2| is quickly brought up to the desired temperature, and the current may then be turned off and the quenching fluid applied through conduit 3 the same passing through the space 20 to quickly cool the heated surface and bring about the desired changes in the metal.

In the modification of the invention as disclosed in Figures 3 to 5, the secondary circuit includes the workpiece so that the heating current passes through the workpiece conductively, As

shown in Figure 3 in section, the workpiece 5U, which is to be heat treated, is cylindrical in shape with a central axial opening and having the section 5| cylindrically uniform and the upper seotion 52 partly curved and partly cylindrical. The particular shape of the annular opening of the workpiece is not material to the invention. The casing of mica 53 electrically insulates the inner surface of section 5 I.

Extending through the annular opening, through the workpiece 5D, including sections 5| and 52, is a conductor tube 54, the same being for the most part of uniform cross section but at the lower end 8 being constructed to enter the narrower opening section 5| of the workpiece. The end of the tube 54 at its base projects beyond the workpiece and is screw-threaded to receive the work-supporting block 55. This block is provided with a recess 56 immediately below the workpiece section 5|, the recess being bound by an upwardly projecting contact ring 57 which bears on the workpiece base outside of the mica shell 53. The base of the block 55 in alignment with the end of the tube 54 is also recessed as at 58 so as to reduce the length of material in the block necessary to be threaded. rl`he central external surface of the block is cut away to form a channel 5S which is enclosed by a shell 68 fixedly attached to the ends of the block thus forming an inner circumferential cavity for the reception of cooling fluid. The tubes 6|, 62 provide means for forcing the coolant through the cavity 59 for cooling the support block 55. The block is also provided with an inlet conduit 63 leading into a recess 55 at the upper end of the block this connecting with the space E4 between the tube 56 and the workpiece. By this means quenching fluid is introduced in the heated areas of the workpiece.

Electrical contact with the upper edge of the workpiece is made by means of a series of contact fingers 55 which bear in a circular' area of the upper surface of the workpiece adjacent but displaced from the tube 54. These fingers, as better shown in Figure 5, are formed by radially sectioning the centrally apertured base 6B of a copper, or hardened copper, cup shaped member 61, the various ngers 65 consequently having a degree of yield because of this construction. Firm pressure of these yieldable fingers on the upper workpiece surface is obtained by use of an auxiliary spring pressure member 68, this member being cylindrical, in conformation with the wall 67a of the contact unit, and adapted to be positioned within the same and secured thereto. The base of the member 58 is radially slotted to form spring fingers 39 the ends of which are down turned to engage yieldingly the fingers E5 of the contact unit. By this means firm but yielding electrical contact is secured between the fingers 65 and the upper surface of the workpiece.

Means are provide for cooling the Contact member 6?. This is accomplished by circumferentially channelling the wall Gla of the contact member and closing the by means of a cylindrical strip to form a c Into this cavity is led a coolant duct 'I2 appropriately coupled by the clamp '53 to the tubing 75. From the cavity 7| the cooling fluid is led through a series of reverseiy coiled tubes connected in circular relation to the base of the cavity 1| and extending in inward section '|15 and. the outward section 'IT intimate contact with the bottom surface of the lingers 65 to which they may be brazed or otherwise attached. By this means cooling by conduction of the contact iingers is accomplished.

The workpiece 58, support block 55 and contact member 61 are combined in a unified Whole by means of a top plate 15, a base plate 16 and connecting bolts 11 with spacers 19 between the plates. These plates may be made of copper, steel or similar metal. The base plate 16 is centrally apertured and provided with a cylindrical holding tube 19 welded or otherwise fastened to the base plate. This tube 19 is preferably of a diameter such as to insure fairly close fit of the workpiece exterior. The upper plate is also apertured to receive a tube 88 which extends appreciably above the plate, to which it is soldered or otherwise attached. To the upper end of tube 89 a secondary terminal plate 8| is fixed the inner end of the terminal being apertured to enclose the end of tube 89 and the outer end being formed in a terminal block 82a. The other terminal 82 is placed directly above the terminal 8| and is supported by a ring connection thro-ugh the insulator tube 83 to the conductor tube 54. Also support is secured by means of bolts 8d passing through insulation liners 85 in the terminal 82, through insulation block 83, and directly engaging the terminal 8| by screw threaded connection.

Electrical connection between the terminal 82 and the central tube 54 is made by means of flexible bus bars 86 which are applied to the outer end of the terminal 82 and clamped to the tube 54 between the insulation block 81 and washer 88. The Washer 88 is xed to the tube 54 so that the current flow is from the bus bars through the washer to the tube. On reference to Figure 4 it will be seen that the insulation block 81 of Fig. 3 is extended outwardly to form an arm 89 which overlies an extension 99 from the inner end of terminal 8| and connection is made between these two elements 89 and 98 by means or a pin 9| movable through the block 89. The pressure washer 92 supports a coil spring 93 and moves with the member 94 in threaded engagement with the terminal extension 90. By this construction adjustment of member 94 upwardly tends to force yieldingly the contact block 55 and the contact member 81 against the lower and upper sides of the workpiece, respectively, so that by this means a unified assembly of the heating unit is obtained. Current is supplied to this unit by means of the transformer 95 having the usual primary 96, core 91 and secondary 98, the latter contacting with the terminal blocks 82a. and 99, respectively.

In utilizing the heating unit as above described in Figures 3, 4 and 5 current, preferably of high amperage and high frequency, is applied to the circuit including the secondary 98, terminal 8|, contact member 61, workpiece 50, contact block 55, tube 54, bus bars 86 and terminal block 99. Thus the circuit is conductive with reference to the workpiece 50, the flow of current being axial in this member. It is pointed out that the contact ring 51 of block 55 engages the workpiece adjacent the surface of the opening 5| of the workpiece and that likewise the contact ngers 65 engaged the workpiece adjacent the central opening. Thus, the shortest path between the contacts at the top and bottom of the aperture 7o is adjacent the aperture and hence there should be maximum density of current flow in this annular space. It is further pointed out that, due to the fact that workpiece and adjacent tube 54 simultaneously conduct current in opposite directions, current iiow is increased at the adjacent conducting surfaces of workpiece and tube 54 due to the neutralization of magnetic effect arising from the counteriiow of current. Consequently, the increase of current due to proximity eect combines with the normal increment of current due to skin effect and develops in the inner surface of the workpiece a high density of current with resultant pronounced heating effect. Particular attention is directed to the fact that the current flow is substantially uniform concentrically along the inner surface of apertures of 5i and 52 of the workpiece, and that the current is not concentrated along a side o1' sector of the apertured surface. This is due to the employment of the circular base contact 51 and the employment of the annular group of spring contacts which effectively distributes the current ow, particularly around the interior surface of the workpiece. Unless this is accompiished, the heating effect is uneven and the result produced is unsatisfactory. After heating the workpiece surface to the desired temperature, the current may be turned off, a quenching iiuid immediately applied to the inlet duct 63, the fluid rising up through the space 64 and overiiowing through the spaces between the contact iingers 65, or between 54 and 80.

In inserting the workpiece for treatment in a heating unit as above described, it is necessary only to remove the contact block when the workpiece may be inserted or removed.

While I have described forms of the invention and details of structure which may be preferred, modiiications may be made therein and hence no limitations are implied other than is required by the scope of the claim hereto appended.

What is claimed is:

An inductive heating unit comprising a tubular electrically conducting shell, a heating conductor extending axially through the shell to a point of attachment on the shell adjacent an end thereof forming a series connection, means for insulatingly supporting a tubular metal workpiece adjacent to, concentric with, but electrically disconnected from said conductor and shell, and terminal connectors secured to the shell and heating conductor at ends thereof opposite to the series connection.

HAROLD A. STRICKLAND, J R.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,436,891 Moody Nov. 28, 1922 2,066,668 Bennett Jan. 5, 1937 2,248,280 Nobron July 8, 1941 2,020,276 Crawford Nov. 5, 1935 2,356,150 Denneen et al Aug. 22, 1944 2,144,378 Kennedy Jan. 17, 1939 FOREIGN PATENTS Number Country Date 435,343 British Sept. 19, 1935 OTHER REFERENCES Babat, Construction of Heating Coils for Induction Surface Hardening, Heat Treating and Forging, Feb. 1941, page 90. (Copy in Scientific Library.) 

